Measuring Forces Applied During Skull Base Surgery
At some time in their lives, 1 in 5 people will have a pituitary tumor, and 1 in 600 of
these will have the tumor grow large enough (>1 cm in diameter) that surgical resection is
required. Traditionally, surgery to remove pituitary tumors or other tumors at the skull
base requires transcranial or transfacial access. In these approaches, large traumatic,
often disfiguring, openings must be created in the patient's forehead or cheek. Endonasal
skull base surgery reduces invasiveness resulting in less trauma, fewer complications, and
shorter surgical time. However, despite the compelling advantages for the patient, only a
small percentage of skull base surgeries are done endonasally. While exact statistics are
not available, the current best estimate in the literature is that less than 50% and most
likely less than 20% of these tumors are addressed by endonasal surgery.
The endonasal approach is underemployed despite its demonstrated benefits to the patient
because existing surgical instruments have limited dexterity and approach angles, and
simultaneously manipulating several of them through a nostril while performing complex
surgical procedures is so technically challenging that only a small number of expert
surgeons can accomplish it. Even for these experts, mortality rates are non-negligible
(0.9%), and there remain contraindications to the endonasal approach, including occlusion of
the surgical site by delicate and critical neurovascular structures (e.g. carotid arteries,
optic nerves), inability to fully reconstruct the dura due to lack of surgical tool
dexterity, and long surgical duration. All of these contraindications are directly related
to limitations in instrument dexterity and visualization, which motivates the development of
a robotic system for endonasal skull base surgery. Such a robot can potentially increase
surgical dexterity and reduce the technical complexity of the procedure for surgeons,
thereby increasing the percentage of patient who benefit from the endonasal technique.
While many robotic systems have been developed for intravascular interventions as well as
natural orifice surgery though other orifices, comparatively few systems have been targeted
at endonasal surgery. This is likely due to the smaller size of the nasal cavity and nostril
compared to other natural orifices.
For endonasal robots, the limited space available in the nostril opening, combined with the
need to work dexterously within the cavities in the head, implies that instrument shafts
must be small in diameter while enabling dexterous motions of instrument tips. A recently
invented robot design that matches these characteristics is the concentric tube robot
concept, which is also known as by the name active cannula.
A robot suitable for endonasal surgery is being developed (see reference #3), however in
order to optimize this robotic system, intraoperative data must be obtained to determine how
the robot interacts with the patient's tissues. The aim of this study is to modify a
traditional tool used in the operating room to allow determination of forces at the skull
base on both hard and soft tissues. This surgical curette will be used in the standard
fashion during endonasal skull base surgery, however will provide valuable information.
The modified curette will consist of two segments joined by a Nano17 6-axis force sensor.
(Image 1) The force sensor is integrated into the shaft of the instrument (a standard
neurosurgical ring curette) and insulated from the shaft with two polyetherimide (also known
as ULTEM) disks so that no current can be transmitted from the force sensor to the curette.
The sensor is held to the shaft by medical grade adhesive and set screws.
The patients will be recruited from the PIs clinical practice. Informed consent will be
obtained. At the appropriate time during surgery this curette will be used to collect force
date. This force transducer operates at 5V (4.8-9V range). These transducers are commonly
used in medical and dental research (see reference #5).
No additional operating room or anesthesia time will be required.
Observational Model: Case-Only, Time Perspective: Prospective
6-axis force and torque data from routine endoscopic transnasal skull base surgery
This data will be collected and recorded via a computer interface with our sensorized tool and recorded in standard units for force and torque. We will also look at the variability of forces between patients after collecting this data. The data will be useful in optimizing a robotic system for endonasal surgery as described in the secondary outcome measure.
Robert Webster, PhD
United States: Institutional Review Board
|Vanderbilt University Skull Base Center||Nashville, Tennessee 37212|